Combination pouch and release sheet and method for producing same

ABSTRACT

An improved release sheet for use in connection with a sanitary catamenial pad is disclosed. The improved release sheet exhibits superior noise, drape, bulk and gloss characteristics due to its method of production. A polyethylenic release material containing silicone capable of being fixed within the surface of the release material is coextruded with at least a base film to provide a film which is also embossed to provide a combination pouch and release sheet with superior physical characteristics. Corona treatment of the release material layer preferably occurs following embossing, but can occur prior to embossing or both prior to and following embossing to fix the silicone within the surface of the release material. In-line recycling of materials provides additional cost advantages.

BACKGROUND OF THE INVENTION

Polyolefins and particularly polyethylenes are good base materials forfilms, coatings and release films. Such materials are easily formulatedinto films which exhibit desired slip, release, peelability and relatedcharacteristics. These films are known in the form of release filmsapplied to adhesive materials, such as removable protective layers foradhesive strips and the like. The protective layer prevents prematureadhesion from the strip and protects the covered area from dust,contamination, etc.

Polymer blends containing silicone are advantageous in the production ofrelease films. However, films containing silicone have traditionallysuffered from movement of the silicone within the film layers or acrosslayers, also known as “migration”. For example, polyolefinic filmscontaining silicone suffer from the tendency for the silicone to migratefrom the surface of the film. Since it is the presence of silicone atthe surface of the film which imparts desired physical characteristics(e.g., slip, release) to the film, any movement of the silicone awayfrom the surface diminishes, if not completely removes, suchadvantageous characteristics.

Although the use of high dose corona treatment is known to inhibitmigration of silicone within the surface of a film, the prior art doesnot disclose, teach or suggest the use of corona treatment incombination with embossing to substantially enhance the performancecharacteristics of silicone-containing polymeric films.

It has been discovered that the use of embossing techniques incombination with corona treatment of a silicone-containing polymericfilm substantially improves the performance characteristics of such filmas a release sheet. Such improved characteristics include lower peelforces, lower noise generated during the peel process, improved drapeand tactile properties and increased bulk.

Traditional approaches to release films designed for use in connectionwith personal hygiene products include coated films and papers, whichinvolves coating a paper with silicone and adhering it to a film.However, such traditional release films suffer from relatively high peelforces and inferior noise, drape and bulk characteristics. Moreover,such traditional, inferior performing films are relatively expensive.

Thus there remains a need for an economical polyethylenic-based film foruse as a combination pouch and release sheet in connection with personalhygiene products, such as sanitary catamenial pads, which is capable ofbeing extruded or coextruded with silicone and exhibits improvedperformance and aesthetic characteristics, and a method for producingsame.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided an improvedcombination pouch and release sheet composed of a silicone-containingembossed polyolefinic material. The film is corona treated to preventmigration of the silicone material within the film. Since the inventionavoids the traditional need for a separate release paper and is producedusing an in-line process, the combination pouch and release sheet of thepresent invention exhibits superior performance while being lessexpensive than such traditional release sheets.

The improved combination pouch and release film of the present inventioncomprises a single- or multiple-layer film. Preferably, a polyolefinicmaterial containing a silicone component is used as a release material.The release material is extruded or coextruded with at least apolyolefinic film not containing silicone using traditional methods.Following extrusion (or coextrusion), the film is embossed to impartsuperior physical and aesthetic characteristics to the film. The releaselayer is then corona treated to prevent migration of the silicone inrelease layer. Corona treating the film either prior to or followingembossing is contemplated by the combination pouch and release sheet ofthe present invention. Preferably, the film is embossed first and thencorona treated; however, as previously mentioned, the film can be coronatreated at any point, and even at multiple points, of the process.Embossing is accomplished via traditional embossing methods.

The resulting film exhibits superior drape, texture, gloss, noise andpeel force characteristics. Moreover, unlike many release films, thesuperior release properties of the release film of the present inventionare not diminished over time in contact with a pressure sensitiveadhesive.

According to a method of the present invention, the improved combinationpouch and release film of the present invention is produced by extrudinga thin layer of a polyolefinic release material containing a siliconecomponent. In one embodiment, the polyolefinic material containingsilicone is coextruded onto a base film (preferably ofnon-silicone-containing polyolefin) to form a film and subsequentlytreated with a corona discharge. Corona treatment prevents the siliconematerial from migrating within the film. Either before or after coronatreatment, but preferably before, the film is embossed to enhance therelease, tactile and aesthetic characteristics of the resultant film.Again, the corona treatment step can even occur at multiple steps withinthe process either before and/or after embossing.

In another embodiment of the method of the present invention, a releasematerial containing silicone and a base material not containing siliconeare coextruded with a base film (also not containing silicone) to forman upper layer (release material), a core layer (base film) and a lowerlayer (base material). The multilayered film is then preferablyembossed. Following embossing, the release material layer is subjectedto corona treatment to fix the silicone within the release material. Asdiscussed above, the release material layer can be corona treated toprevent migration of the silicone prior to embossing, and can even becorona treated both prior to and following embossing.

Due to the in-line corona treatment of the film, there is no need forthe time and expense associated with the traditional steps of coatingand curing the film. The present method features in-line recycling ofthe process remnants from the film into the core layer, thus providingyet additional cost savings. Remnants from the film of a two layercoextrusion are recycled into the base film.

BRIEF DESCRIPTION OF THE FIGURES

A more complete understanding of the present invention may be had byreference to the following detailed description when taken inconjunction with the accompanying figures wherein:

FIG. 1 is an unembossed, corona treated silicone-containing flat releasefilm; and

FIG. 2 illustrates a two-layer embodiment of the improved combinationpouch and release sheet of the present invention; and

FIG. 3 illustrates a three-layer embodiment of the improved combinationpouch and release sheet of the present invention.

DETAILED DESCRIPTION OF FIGURES

A combination pouch and release sheet is provided which exhibitssuperior physical characteristics, such as low gloss and low noise andimproved release, drape and bulk. These superior physicalcharacteristics are due to the unique combination of corona treatment ofa silicone-containing film together with embossing of the film beforeand/or after such corona treatment.

In FIG. 1, there is shown a traditional unembossed release sheet 10,having a release layer 20 and a base layer 30. Since the traditionalrelease sheet 10 is unembossed, it does not exhibit the superiorphysical and aesthetic characteristics of the improved combination pouchand release sheet of the present invention.

In a preferred embodiment, illustrated in FIG. 2, the improvedcombination pouch and release sheet 40 of the present invention is of atwo layer construction having a relatively thick (approximately 90% ofthe total thickness of the film) base film layer 50 and a relativelythin (the remaining approximately 10% of the total thickness) releaselayer 60. The relatively thick base film layer 50 is preferablyconstructed of a silicone-free polyolefin polymer, such as a ethylenichomopolmer or copolymer. Mixtures and blends of the foregoing materialsmay also be used, if desired. Such materials are preferred because theyexhibit desired embossing characteristics. These materials are notintended as an exhaustive list of acceptable materials.

The silicone present in the relatively thin release layer 60 can belocked into place using corona treatment. An example of a preferredsilicone-containing thin release layer 60 material for the improvedcombination pouch and release sheet 40 of the present invention is asilicone-containing polyethylene known as BYNEL 534, available fromDupont Canada.

Additionally, additives such as stabilizers, anti-block and slip agentsmay be added to the material comprising the base film layer 50. Fillers,such as titanium dioxide, mica, calcium, talc and the like, and pigmentsor dyes may also be added, as desired.

In the preferred embodiment, the improved combination pouch and releasesheet 40 is composed of two or more layers coextruded using traditionalmethods known in the art. Coextrusion of the two or more layers cojoinsthe layers by forming a strong bond between the individual layers.Although a multilayered embodiment is preferred, it is noted that amonolayer embodiment extruded using techniques known in the art is alsocontemplated by the present invention.

The coextruded film is subjected to corona treatment to prevent themigration of the silicone material from the polyolefinic material of thethin release layer 60. Corona treatment chemically locks the siliconeinto the relatively thin release layer 60 through ionic attraction suchthat migration of the silicone is thereafter prevented. Since it is thepresence of the silicone material in the surface of the relatively thinrelease layer 60 of the film which provides many of the superiorphysical properties of the improved release sheet, it is important thesilicone material remain fixed in the surface and does not travel orotherwise migrate during or after production of the film. The stationarysilicone material also provides the resultant release sheet withsuperior release properties unaffected by time in contact with apressure sensitive adhesive. Corona treatment may be accomplished usingtechniques known in the art, such as by passing the film between agrounded cylindrical electrode and an overlying high potential electrodewhich form an arch over the grounded roll.

Embossing of the coextruded multilayered film can be carried out toaffect varying degrees of embossing. Substantial performance andaesthetic improvements have been discovered both where the film is“shallow” embossed (e.g., 30% increased low load caliper) and where“deep” embossing (e.g., up to 100% increase in low load caliper) isaccomplished. Various degrees and geometries of embossing can beemployed within the scope of the present invention.

The resultant improved combination pouch and release sheet 40 exhibitsup to 85% less peel force than traditional release sheets, 30-100% morebulk than nonembossed release sheets and superior noise and drapecharacteristics, both highly important in the personal hygiene productapplications, such as pouches for sanitary napkins.

As illustrated in FIG. 3, another embodiment of the improved combinationpouch and release sheet 70 of the present invention comprises threelayers. A relatively thin release material layer 80, a relatively thickbase film 90 and a relatively thin base material layer 100 comprise thisembodiment. The base film layer 90 is analogous to the base film layer50 of the preferred embodiment described above and is constructed of asilicone-free polyolefin polymer, such as a ethylenic homopolmer orcopolymer. Likewise, the thin release layer 80 is preferably constructedof a material containing silicone. The silicone present in therelatively thin release layer 80 can be locked into place using coronatreatment. As with the preferred embodiment, the silicone-containingpolyethylene known as BYNEL 534 is a preferred material for the thinrelease layer 80. The embossing technique, additives,extrusion/coextrusion techniques for the three layered embodiment are asdescribed above for the preferred two-layer embodiment.

With the three-layered embodiment, in-line recycling of the processremnants into the core layer of the combination pouch and release sheet(rather than the base film) is accomplished. This feature provides addedcost reduction to the resulting combination pouch and release sheet.

According to a method of the present invention the above-identifiedimproved combination pouch and release sheet is produced by employingthe steps of: preselecting a release material, preferably apolyethylenic material containing silicone which can be locked intoplace within the surface of the material; preselecting a base film foruse with the release material, preferably a polyethylenic material notcontaining silicone; coextruding a thin layer of the release materialcontaining silicone with a layer of the base film; and subjecting thetop layer (release material) to corona treatment to prevent migration ofthe silicone material either before or after or both before and afterembossing the resultant multilayered film to impart superior physicalcharacteristics.

A different embodiment of the method of the present invention includesthe following steps; preselecting a release material containingsilicone; preselecting a base material not containing silicone;preselecting a base film not containing silicone; coextruding the basefilm between an upper layer of the release material and a lower layer ofthe base material such that the base film, or core layer, is sandwichedbetween the upper layer (release layer) and the lower layer (basematerial); subjecting the upper layer (release material) to coronatreatment to prevent migration of the silicone material either before,after or both prior to and following embossing the resultantmultilayered film to impart superior physical characteristics.

An ideal product category for use of the improved release sheet of thepresent invention is the personal hygiene industry, including sanitarycatamenial pads and the like. The increased bulk, low noise, low glossand superior drape make the improved release sheet ideal for use as acombination pouch and release sheet for such products.

One of the superior physical characteristics of the combination pouchand release sheet of the present invention, improved release values, isillustrated in the following table.

TABLE I 180 Degree Peel Test Sample Max. Peel Strength Min. PeelStrength Avg. Peel Strength No. grams/in. grams/in. grams/in. 3 25.121.8 23.6 5 25.2 21.2 23.7 11 15.4 12.8 13.7 13 18.8 18.2 18.5

In Table I above, film Samples Nos. 3 and 11 are the same film, preparedusing the same production process, except that Sample 3 was leftunembossed and Sample 11 was embossed. Likewise, film Samples Nos. 5 and13 are identical films, prepared according to the same productionprocess, except that Sample No. 5 was left unembossed and Sample No. 13was embossed. The samples were then subject to peel strength testing at180 degrees in accordance with Tribble Release Test Standard. The amountof force necessary to peel the samples was then measured and recorded ingrams. Sixteen measurements for each film was recorded.

As demonstrated in Table I, Sample Nos. 11 and 13, the embossed filmsamples, demonstrated superior peel strength numbers in that less forcewas required to peel the embossed film samples, Sample Nos. 11 and 13,than was required with the unembossed samples, Sample Nos. 3 and 5.

It is important to note that release values noted above are for filmsprepared according to the present invention method, except for SampleNos. 3 and 5, which were not embossed. Traditional films not preparedaccording to the method of the present invention exhibit peel strengthvalues of approximately 60 grams/in., or approximately three-four timesthat exhibited by the improved combination pouch and release sheet ofthe present invention.

Although preferred embodiments of the invention have been described inthe foregoing Detailed Description, it will be understood that theinvention is not limited to the embodiments disclosed, but is capable ofnumerous rearrangements and modifications of parts and elements withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A sheet having improved release properties, saidsheet comprising: a release material containing silicone; a base film;said release material coextruded with said base film to form amultilayered release film; said release material corona treated to fixinto position on a molecular level said silicone; and said release filmincluding an embossed surface.
 2. The sheet of claim 1, wherein therelease material is a polyolefin.
 3. The sheet of claim 1, wherein therelease material is a polyethylemic polymer.
 4. The sheet of claim 1,wherein the base film is a polyolefin.
 5. The sheet of claim 1, whereinthe base film does not contain silicone.
 6. The sheet of claim 1,wherein the base film comprises a polyethylenic material.
 7. The sheetof claim 1, wherein the multilayered release film is embossed.
 8. Thesheet of claim 7, wherein said release material is corona treated afterthe release film is embossed.
 9. The sheet of claim 7, wherein saidrelease material is corona treated before the release film is embossed.10. The sheet of claim 7, wherein said release material is coronatreated both prior to and following embossing of the release film. 11.The sheet of claim 1, wherein the sheet is used in connection with acombination pouch and release sheet for a sanitary catamenial pad. 12.The sheet of claim 1, wherein the base film is comprised of a polyolefincontaining silicone.
 13. A combination pouch and sheet having improvedrelease properties, said combination pouch and sheet comprising: anupper layer comprised of a polyethylenic polymer release materialcontaining silicone; a core layer comprised of a polyolefin base filmnot containing silicone; a lower layer comprised of a polyolefin basematerial not containing silicone; said core layer coextruded with saidupper layer and said lower layer to form a multilayered release film;said upper layer corona treated to fix into position on a molecularlevel said silicone; and said multilayered release film embossed toprovide said sheet.
 14. The combination pouch and sheet of claim 13,wherein the core layer is comprised of a polyolefin base film containingsilicone.
 15. A method for the production of a sheet having improvedrelease properties, said sheet comprising the steps of: preselecting arelease material; preselecting a base material; preselecting a basefilm; coextruding a layer of said release material and a layer of saidbase material on opposing sides of a layer of the base film to form arelease film; embossing the release film to provide improved physicalcharacteristics; and corona treating the surface of the release materiallayer of the release film.
 16. The method of claim 15, wherein the stepsof preselecting a release material and a base material include theselection of polyolefins.
 17. The method of claim 15, wherein the stepof preselecting a release material includes the selection of apolyethylenic polymer containing silicone.
 18. The method of claim 15,wherein the step of preselecting a base material includes the selectionof a polyethylenic polymer not containing silicone.
 19. The method ofclaim 15, wherein the step of preselecting a base film includes theselection of a polyolefin.
 20. The method of claim 15, wherein the stepof preselecting a base film includes selection of a polyethylenicpolymer not containing silicone.
 21. The method of claim 15, wherein thesheet is used as a combination pouch and release sheet for a sanitarycatamenial pad.
 22. The method of claim 15, wherein the release materiallayer is corona treated after the sheet is embossed.
 23. The method ofclaim 15, wherein the release material layer is corona treated beforethe sheet is embossed.
 24. The method of claim 15, wherein the releaseis corona treated both prior to and following embossing the sheet.
 25. Amethod for the production of a sheet having improved release properties,comprising the steps of: preselecting a release material ofpolyethylenic polymer containing silicone; preselecting a base film ofpolyethylenic polymer not containing silicone; coextruding at least onelayer of said release material onto a layer of said base film to form arelease film; embossing said release film; and corona treating thesurface of the release material layer of the release film to fix intoposition on a molecular level the silicone.
 26. The method of claim 25,wherein the sheet is used as a combination pouch and release sheet for asanitary catamenial pad.
 27. The method of claim 25, wherein the releasematerial layer is corona treated after the release film is embossed. 28.The method of claim 25, wherein the release material layer is coronatreated before the release film is embossed.
 29. The method of claim 25,wherein the release material is corona treated both prior to andfollowing embossing of the release film.
 30. The sheet of claim 1,wherein said release material layer is less than about 10% of the totalthickness of said multilayered release film.
 31. The combination pouchand sheet of claim 13, wherein said upper layer is less than about 10%of the total thickness of said multilayered release film.
 32. Thecombination pouch and sheet of claim 31, wherein said lower layer isless than about 10% of the total thickness of said multilayered releasefilm.
 33. The method of claim 15, wherein the layer of said releasematerial is less than about 10% of the total thickness of said releasefilm.
 34. The method of claim 33, wherein the layer of said basematerial is less than about 10% of the total thickness of said releasefilm.
 35. The method of claim 25, wherein the layer of said releasematerial is less than about 10% of the total thickness of said releasefilm.